How does a breathalyzer work?

On Behalf of | Feb 6, 2024 | Drunk Driving

New Jersey, like most other states, has enacted a statute that prohibits all persons who operate a motor vehicle on the state’s highways from driving with a blood alcohol content (“BAC”) greater than 0.08%. Most states have similar limits.

The limit on BAC effectively defines the meaning of intoxication for the purposes of charging and convicting persons suspected of driving under the influence of alcohol (“DWI”) in New Jersey. New Jersey law also gives law enforcement officers the power to demand that a driver suspected of driving while intoxicated submit to what is called a “breathalyzer” test.

A police officer making such a demand usually asks the suspected drunk driver to breath into a device called a “breathalyzer.” The breathalyzer is designed to detect the amount of alcohol in the driver’s bloods stream. This post is intended to explain in non-technical terms how a breathalyzer measures alcohol in a person’s blood stream.

The basic components of a breathalyzer

The essential components of a breathalyzer are a mouth-piece, two chambers that hold potassium chromate, liquid that changes color to a shade of light green depending upon the amount of alcohol present in the liquid. The final element of the breathalyzer is a photoelectric cell that creates a signal that is displayed on the face of the breathalyzer.

How the breathalyzer produces a BAC reading

The person being tested must breathe into the mouthpiece of the breathalyzer. The person’s breath is then passed through one of the two chambers filled with potassium chromate. The other chamber does not receive a sample of the driver’s breath and is used as a control.

The photoelectric cell reads the difference in color change between the two test chambers and creates an electronic signal that can be read on the face of the breathalyzer. Most breathalyzers report the results as “pass” – a BAC of less than 0.08%, “fail” – a BAC of more than 0.08%, or “invalid” – measurement was read by the photoelectric cell as not accurate.

Consequences of refusing a breath test

Refusing a proper request to take a breath test can result in the temporary loss of driving privileges, and some experienced attorneys advise their clients to refuse a request for a breathalyzer.

However, other attorneys believe that many breath tests are defective and can be excluded from evidence under aggressive cross-examination.


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